1. Field Of The Invention
The invention herein pertains to controlling the deletrious effects of silica during metal deposition and particularly pertains to controlling silica effects during the electroless deposition of silver on glass substrates.
2. Background And Objectives Of The Invention
Silica (SiO.sub.2) occurs naturally and is the most common of all chemicals compounds. Silica is contained in most water as it is derived from dissolved silicate materials. Silica is extremely detrimental to metal deposition or plating processes at 0.5 parts per million (ppm) or more and in the mirror industry, the effects of excess silica can be seen as a reduction in plating efficiency (the amount of silver deposited per square foot of glass) to a partial or even a complete inhibition of the plating process. In extreme cases, plating is disrupted to the point that no metal is deposited and as a consequence, mirror manufacturers generally install complex and expensive water purification systems to remove silica and other impurities which may be present in the water supply. Such purification systems usually employ ion exchange resins including mixed cation and anion resins and activated carbon. However, when these exchange resins approach their capacity, silica will begin to be released in small and then larger amounts (ppm). The amounts of silica released after exchange resin saturation can be in far greater concentrations than in the untreated water and as such, can cause havoc to the plating process. As a result, many plating operations have implemented monitoring procedures to determine increases in silica amounts. However, such monitoring does not quickly respond and the plating reaction deteriorates rapidly before defensive actions can be taken, causing the mirror substrates to have large unplated areas or voids. Once these voids have been detected by visual inspection the plating lines must be shut down and the ion exchange resins regenerated or replaced in order to continue production. Oftentimes many hundreds or even thousands of dollars can be wasted by failure to quickly determine the silica increases. As the mirror plating industry is very cost conscious and price competitive even a very short production of poor quality plating will waste expensive plating solutions, glass and workers' time. Regeneration of the water purification systems will likewise cause additional expense if conducted more than necessary to minimize the capture of excess silica (herein defined as amounts over 0.5 ppm).
Thus, with the problems and disadvantages of conventional metal plating processes in handling excess silica concentrations, it is an objective of the present invention to provide a means to control the available silica and its adverse effects in metal plating solutions.
It is also an objective of the present invention to provide a number of chemical compounds which can be added to conventional plating solutions to combat and control the effects of excess silica.
It is also an objective of the present invention to provide an amine compound which will control the harmful effects of silica in plating solutions.
It is still another objective of the present invention to provide a metal plating solution that will perform well with high concentration of silica present.
Various other objectives and advantages of the present invention will become apparent to those skilled in the art as a more detailed description is set forth below.